This application claims priority to Japanese Patent Application 2006-017531 filed on Jan. 26, 2006, hereby incorporated by reference.
The present invention relates to a twin roll casting machine.
It is known to cast steel strip by continuous casting in a twin roll caster. In this technique molten metal is introduced between a pair of counter-rotated horizontal casting rolls, which are cooled so that metal shells solidify on the moving roll surfaces, and are brought together at a nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of vessels from which it flows through a metal delivery nozzle located above the nip, for forming a casting pool of molten metal supported on the casting surfaces of the rolls above the nip and extending along the length of the casting rolls. This casting pool is usually confined between side plates or dams held in sliding engagement adjacent the ends of the casting rolls so as to restrict the casting pool against outflow.
FIG. 5 and FIG. 6 illustrate an example of a known twin roll type casting machine. The machine comprises a pair of water-cooled casting rolls 1 positioned laterally to form a roll nip G between them, and a pair of side plates 2 engage the ends of the casting rolls 1.
The direction and speed of rotation of the counter-rotating casting rolls 1 are set so that the outer circumferential surfaces of the casting rolls move from above towards the roll nip G. One of the side plates 2 is in contact with the ends of the two casting rolls 1 at one end of the rolls, and the other of the side plates 2 is in contact with the ends of the two casting rolls 1 at the other end of the rolls 1. A molten metal delivery nozzle 4 made from a refractory material is positioned above the roll nip G in a space enclosed by the casting rolls 1 and the side plates 2.
The molten metal delivery nozzle 4 comprises side walls and end walls that define an upwardly opening elongated trough 6 for receiving molten metal 5 and a plurality of outlet openings 7 for outflow of molten metal from the trough 6. The openings 7 are formed in a lower section of the side walls of the nozzle 4 to direct molten metal from the trough 6 towards the outer circumferential surfaces of the casting rolls 1. With this arrangement, molten metal 5 poured into the trough 6 flows outwardly through the openings 7 and forms a casting pool of molten metal 8 in contact with the outer circumferential surfaces of the casting rolls 1 over the roll nip G.
When the casting pool 8 is formed and the casting rolls 1 are rotating with cooling water flowing through and extracting heat from the rolls 1, molten metal 5 solidifies at the outer circumferential surfaces of the casting rolls 1 and forms solidified shells. A downwardly moving strip 3 is formed by the solidified shells coming together at the roll nip G.
The spacing between the casting rolls 1 at the roll nip G is maintained by horizontally acting thrust forces F that are applied to roll end support structures (not shown) that support the ends of the casting rolls 1 to bring them together to form a strip 3 of a desired thickness delivered downwardly from the roll nip G.
The thrust forces F are selected to be sufficient to counter (a) the ferrostatic pressure that acts on the casting rolls 1 through the molten metal 5 in the casting pool 8, (b) friction between the movable casting roll or rolls 1 and a guide assembly that supports the roll(s) for horizontal movement towards or away from each other, and (c) unbalanced “rogue” forces acting on the casting rolls 1.
The unbalanced “rogue” forces may be caused by a number of factors, including (a) a non-uniform distribution of the mass of the casting rolls 1, including the auxiliary parts, such as rotary joints for supplying cooling water to and removing cooling water from the rolls and so forth and (b) the effects of cooling water flowing into, through, and from the casting rolls 1. However, unbalanced rogue forces are undesirable from the viewpoint of process control and product quality. Moreover, increasing thrust forces F may not always compensate for adverse effects of rogue forces.
The ferrostatic pressure that acts on the casting rolls 1 through the molten metal 5 in the casting pool 8 is determined by factors, including the diameter of the casting rolls, the length of the roll bodies of the casting rolls 1, the height of the casting pool 8, the speed of rotation of the casting rolls 1, and the composition and temperature of the material used to form strip 3.
We have found that a substantial portion of the thrust forces F should be to account for the ferrostatic pressure of the molten metal 5. It can be shown by calculation that, for a ferrostatic pressure generated by a casting pool 8 of mass 150 kg, the total of the thrust forces F required to counter the ferrostatic pressure should be of the order of 150 kg+α (where α<10 kg). However, in practice in the past, thrust forces F in excess of 300 kg were required in order to counter the ferrostatic pressure and the other factors mentioned above, such as the weight and pressure of cooling water that, typically, is continuously supplied at a rate of 5 tones per minute at 20 m per second to the casting rolls 1.
The required thrust forces F of 300 kg are excessive and can have an undesirable impact on process control and product quality. For example, the excessive thrust forces, particularly if unbalanced along the length of the casting rolls 1, may generate chatter, which results in irregularities in the thickness of the strip 3 along the length and across the width of the strip 3.
Moreover, a non-uniform distribution of the mass of the casting rolls 1, including the auxiliary parts such as the rotary joints, may cause misalignment of the casting rolls 1 such that there is an undesirable variation in the roll nip G along the length of the casting rolls 1. Typically, in such situations, the roll gap G is wedge-shaped when viewed from above along the casting rolls 1, with a larger gap at one end and a smaller gap at the other end of the rolls 1.
The twin roll casting machine of the present disclosure can reduce unbalanced rogue forces and provide better control to produce better quality product.
A twin roll casting machine is disclosed that comprises:                (a) a pair of water-cooled casting rolls laterally positioned to form a nip therebetween, with the casting rolls biased towards each other by thrust forces, and        (b) rotary joints coupled to at least at one end of the casting rolls and capable of supplying cooling water into and removing cooling water out of passages in the casting rolls, with the rotary joints of each casting roll being arranged so that the flow of cooling water into the rotary joints and the flow of cooling water out of the rotary joints exert forces on the casting rolls generally in a direction along the rotational axis of the casting.        
The flow of cooling water into and out of the rotary joints may be a vertical direction that is generally perpendicular to a rotational axis of the casting roll. The rotary joints of the casting rolls may be arranged so that the flow of cooling water into the rotary joints is in a generally vertical upward direction orthogonal to the rotational axes of the casting rolls.
The rotary joints may be coupled to both ends of both casting rolls and capable of supplying cooling water into and removing cooling water out of passages in the casting rolls, with the rotary joints of each casting roll being arranged so that the flow of cooling water into the rotary joints and the flow of cooling water out of the rotary joints exert forces on the casting rolls generally in a direction along the rotational axis of the casting.
When the rotary joints are coupled to only one end of the casting rolls, counterweights may be attached to sections of the casting rolls at the other end of the casting rolls that counterbalance the rotary joints.
The twin roll casting machine may also comprise cooling water supply hoses connected to the rotary joints, and biasing units that apply force to support the hoses such that the mass of the hoses is not carried by the casting rolls. Guides may also be provided that guide the hoses in a radial direction of the casting rolls.
The twin roll type casting machine may also comprise spindles capable of transmitting rotational movement from a rotational drive to drive the casting rolls, and biasing units capable of applying a force upwards to support the spindles such that the mass of the spindles is not carried by the casting rolls. Bearings may be provided to support the spindles, and the biasing units capable of applying a force upwards to support the bearings. Guides may also be provided capable of guiding the bearings in a horizontal direction.
Also disclosed is a method of producing thin cast strip by continuous casting comprising the steps of:                (a) assembling a twin-roll caster having a pair of casting rolls laterally positioned to form a nip between said casting rolls;        (b) assembling a drive system for said twin-roll caster capable of driving said casting rolls in a counter rotational direction;        (c) assembling a metal delivery system capable of forming a casting pool supported by said casting rolls above said nip and having side dams adjacent to an end of the nip to confine said casting pool;        (d) introducing molten metal between said pair of casting rolls to form said casting pool supported on casting surfaces of said casting rolls and confined by said side dams;        (e) counter-rotating said casting rolls to form solidified metal shells on said surfaces of said casting rolls and cast strip from said solidified shells through said nip between said casting rolls; and        (f) applying a thrust force through casting roll support structures on each casting roll to bias the casting rolls together, with a majority portion of the thrust force to counterbalance ferrostatic pressure.        
The step of applying a thrust force may include reducing vertical loads applied on the casting roll support structures.
The step of applying the thrust force comprises introducing cooling water into rotary joints coupled to at least one end of the casting rolls, with the rotary joints capable of supplying cooling water into and removing cooling water out of passages in the casting rolls so that the flow of cooling water into and out of the rotary joints exert forces on the casting rolls generally in the direction along the rotational axis of the casting rolls. The rotary couplings may be capable of flowing the cooling water into and out of the rotary coupling in a generally vertical direction perpendicular to a rotation axis of the casting roll.
The step of introducing and removing cooling water may be performed at both ends of each casting roll. Where the step of introducing and removing cooling water is performed at one end of the casting rolls, the method may further comprise the step of counterbalancing the weight of the rotary joints by applying a counterweight at the other end of the casting rolls.
In the method of producing thin cast strip, the step of applying a thrust force may comprise applying a generally upwards force on cooling water conduits to reduce loads applied on the casting roll support structures by the cooling water conduits.
The method of producing thin cast strip may further comprise transmitting rotary movement from a drive mechanism through a spindle to a corresponding casting roll, and the step of applying a thrust force may comprise applying an upwards force on the spindle such that the mass of the spindle is generally not carried by the associated casting roll.
The twin roll casting machine and method of continuously casting thin strip may provide one or more than one of the following beneficial effects.
The inflow and the outflow of cooling water to and from the rotary joints of the casting rolls is directed generally along the axes of rotation of the casting rolls, with a result that there are reduced unbalanced rogue forces (and consequently reduced thrust forces F needed) compared to the previously known casting machine shown in FIGS. 5 and 6.
The rotary joints generate moments that act on the casting roll and about the adjacent casting roll end support structures that can be counter balanced by each other or by counterweights. In embodiments where counterweights are employed, each counterweight generates a moment that acts on the casting roll and about the adjacent casting roll support structure that are complementary to the moments of the rotary joint at the opposite ends of the casting rolls. The counterweights also assist in distributing the mass of the casting rolls between the roll end support structures when the casting rolls 1 are rotating.
When there are rotary joints at both ends of the casting rolls, upwards directed forces are applied to both ends of the casting rolls, and reduce sliding resistance of the casting roll end support structures that support the casting rolls.
Where cooling water supply hoses are provided and the cooling water hoses are supported by biasing units, the mass of the hoses is not carried by the casting rolls, and the sliding resistance of the roll end support structures that support the casting rolls are reduced.
Where bearings supporting the spindles are biased upwardly and supported to move horizontally, the mass of the spindles is not carried by the casting rolls, and the sliding resistance of the roll end support structures that support the casting rolls are reduced.